


Knocking On Dimensional Walls

by fakeivy



Category: Undertale (Video Game)
Genre: Blow Jobs, Ecto-Genitalia (Undertale), Ecto-Penis (Undertale), Ecto-Tentacles (Undertale), Ecto-Tongue (Undertale), Ecto-Vagina (Undertale), Ectotoys, Face-Fucking, Flavored Cum, Fluff, Fluff and Humor, Fluff and Smut, Fontcest, Fontfest - Freeform, HoneyKetchup, Mating Cycles/In Heat, Multi, Polyamory, Puns & Word Play, Somnophilia, Swapfell Sans, Tentacles
Language: English
Status: In-Progress
Published: 2016-12-16
Updated: 2017-01-30
Packaged: 2018-08-31 12:35:17
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 2,739
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8578750
Author URL: https://archiveofourown.org/users/fakeivy/pseuds/fakeivy
Summary: In which a rattle of skeletons have a relationship.





	1. Chapter 01

**Summary for the Chapter:**

> Pairing: US!PapyrusXUT!Sans

They were both grinning as they headed home from the costume party. The amount of groaning they had received for going as each other had been great.

"surprised no one warmed up to our idea," Sans chuckled, tugging at the orange hoodie he was wearing.

"Yeah, their taste is decidedly lacking," Papyrus agreed, sliding his blue sleeves up to bare his radii and ulnae. Sans glanced sideways at the revealed bones.

"So where to now?"

Sans glanced up to see Papyrus staring back, amusement and something else shining in his eyes.

 _fuck it_ , sans thought.

"home," Sans said, grabbing Papyrus' arm and teleporting them into his bedroom.

Papyrus turned to face him, grin widening.

"And now?"

Sans pulled Papyrus down for a kiss, abruptly sliding his tongue into his mouth. Papyrus raised his hands to cradle Sans' head, tilting to deepen the kiss.

"hah, heh,” Sans broke away, panting. “guess it's your lucky day.”

“My days _are_ special whenever I can spend time with you, but I suspect that's not what you're referring to,” Papyrus said, shifting closer. Sans blushed at the bald admission.

“decided to grant your request.”

Papyrus perked up.

“You mean...?” He brushed his thumbs just under Sans' eyes, slowly edging into his sockets. Sans grabbed his wrists.

“ah, yeah, no-not today, least. you're warm, though,” Sans teased.

Papyrus' eyes gleamed. 

“Here, then?”

He slowly dragged his thumbs down Sans' cheeks to hook into his mandible. Sans obligingly opened his mouth, tongue lolling.

“ye', 'ou gueshed it.”

Papyrus grinned excitedly, before abruptly picking Sans up and dropping him on the bed.

“oof.”

“Then I'd better take care of you first,” he said, kneeling in front of him.

“paps, you don't have to-oh!” Sans groaned as Papyrus' mouth closed around his cock, drawing his shorts and slippers off and throwing them behind him as he circled his tongue around the tip.

“But I want to,” Papyrus replied, magically projecting his voice as he continued to lick and suck.

“mn, but-”

“But nothing,” Papyrus interrupted decisively. He started bobbing up-and-down.

“ah!” Sans convulsed around Papyrus's head from the sudden surge in pleasure, ankles locking around Papyrus' neck.

 _he's syncing his rhythm to the pulses of my soul_ , he dazedly realized, clutching Papyrus' head as the pleasure mounted.

“you...hah...dick...kuh!”

“Yes, yes, I'm a terrible person for finding a way to exponentially increase your pleasure. Sans, let go,” Papyrus urged, speeding up. “No one can be strong all the time...you're the one who taught me that.”

“Papyrus-!”

Sans' grip tightening was the only warning Papyrus got before his mouth was filled with cum. Drinking it down, he slowed his rhythm until Sans' soul stabilized, then with one final lick of the dissolving member he drew away.

Or tried to. The limpet clinging to him prevented him from moving. Sans' pants caused him to shiver.

“Sans? You okay?” His mandible clicked softly against Sans' pelvis as he switched back to talking without magic. He massaged Sans' femurs soothingly.

Sans twitched, before slowly unwinding himself from Papyrus. He fell backwards with a groan, covering his eyes with his arm.

It did nothing to hide his blush.

“talk about a tough act to follow.”

Papyrus settled back on his heels, resting his hands on Sans' knees.

“Did you want to stop here, then?”

Sans moved his arm enough to peek at Papyrus with one eye. He'd expected annoyance, but saw only concern in his earnest expression.

Then he felt it.

“idiot. stop trying to play it cool when i can feel your magic.” He lightly shoved Papyrus' side with his foot. Papyrus blushed, expression turning slightly sheepish.

“Ah, my clever ruse has been foiled. I must admit, then, that my patience is not limitless. My control is quickly running out. So if you're truly spent, I'm going to teleport myself straight into a hot shower.”

Sans snorted, propping himself up on his elbows with a grin.

“good to know i made you all hot and bothered. alright, i've gained back my confidence. face-fuck me to your soul's content.”

Papyrus straightened.

“Are you sure?”

“yep.”

Papyrus rocked to his feet, kicking off his slippers and drawing his shorts off to reveal his twitching cock, before climbing onto the bed to straddle Sans.

“Stop me if it gets to be too much.”

And with that, Papyrus grabbed Sans' skull, lined up Sans' open mouth with his cock, and slammed his cock home, setting a furious pace.

Sans grabbed onto Papyrus' femurs to help stabilize his position so Papyrus could continue to pound into his mouth.

_not as uncomfortable as i thought it'd be. how's paps enjoying it?_

Sans rolled his eyes up to see Papyrus had his eyes clenched shut, pleasure obvious as his chants of Sans' name slowly grew in volume.

Then with a shout, Papyrus came.

Sans swallowed. His eyes widened. With a twist of his magic, he wrenched his head out of Papyrus' grasp.

“what?” He sputtered, one hand coming up to catch the cum dripping from his mouth.

“What's wrong?” Papyrus' hands hovered, unsure if his touch was welcome.

“why's it taste like...”

“Shit, did I mess up?”

Papyrus stole a kiss, tongue thorough. He drew back, worry fading to be replaced with puzzlement.

“No, it's perfect. I thought you liked butterscotch?”

“no-I mean, yes, I do-just...why?”

 _you've never changed the taste before. why now?_ went unsaid.

Papyrus sighed before softly clacking their foreheads together.

“Do I really have to spell it out?” The faintest of blushes suffused his face.

“I'm sweet for you, Sans.”

“oh. _oh~_ ”

Papyrus groaned, hiding his face against Sans' neck as he tumbled them both sideways to lay on the bed.

“Jerk. Knew you would react this way,” he grumbled.

“of course! having the too-cool papyrus fall for me? i'm gonna be bragging about this for weeks. but, hey, look at me. come on,” Sans coaxed. Papyrus reluctantly drew back from his hiding place.

Sans claimed his mouth in a kiss.

Papyrus' mouth was flooded with the taste of honey.

“will you bee my honey?” Sans said once he drew back, grin lopsided.

Surprise fading into delight, Papyrus kissed him again.

“Only if you'll bee mine.”

Snuggling Sans, Papyrus basked in the wonder of his feelings returned.

“...so next time, can you make your cum taste like ketchup?”

“Sans!”

“come on, please?”

“...no promises.”

Papyrus smiled as he listened to Sans' chuckles.

**Notes for the Chapter:**

> Had a blast writing this; I've fallen in love with the honeyketchup ship. It was really fun creating my own interpretation for Underswap!Papyrus.
> 
> The song I listened to this time was [Ready](https://www.youtube.com/watch?v=rYVxPB0ghGE) from the One Piece 'Jango's Dance Carnival' short.


	2. Chapter 02

**Summary for the Chapter:**

> Pairing: UT!Sans/Gaster/(UT!Papyrus,SF!Sans,UF!Sans,US!Papyrus)

**Notes for the Chapter:**

> While using nicknames/endearments is infinitely easier, I love the idea that all the skeletons use everyone's actual names and always know when someone's speaking to them.
> 
> So I've color-coded everyone, though if you decide to hide my work skin, I believe you'll still be able to figure out who everyone is by context.
> 
> UT!Sans   
>  UF!Sans   
>  SF!Sans   
>  UT!Papyrus   
>  US!Papyrus
> 
> It was pretty interesting learning to make my first work skin.

Gaster's voice floated down the hallway.

“Sans?”

“yeah?”

“Could you come he-here?”

Sans climbed off his bed, setting down the book he was reading, and ambled over to the door to Gaster's room.

Sans knocked.

“C-come in.”

Sans opened the door, and stopped.

Gaster had swiveled his chair to face the doorway, putting his body on display. His clothing was rumpled. His robes lay strewn on the floor. His turtleneck was pulled up, just revealing the bottom of his ribcage.

Sans' eyes drifted lower.

“you're looking a little tied up. need a hand?” Sans drawled with amusement after a moment, staring at the mass of tentacles pinning both of Gaster's hands to his pelvis.

“Please, I can't-” Gaster threw his head back with a moan as the tentacles writhed, rubbing against the sensitive insides of the holes on his hands. One tentacle briefly curled around his bottom-most rib, causing him to jerk, before it released him.

Sans stepped closer with a grin, leaving the door open.

“i've got just the thing.”

Sans spread his hands, four objects appearing between his fingers. They were cylindrical, slightly see-through, and glowed different colors; dark orange, red, pale orange, and purple.

“try this one on for size,” Sans said, before sliding the dark orange object onto one of the tentacles.

There was a crash downstairs.

Papyrus's voice indignantly called out:

“SANS! _NOW_?? I'M TRYING TO COOK HERE!”

“sorry, bro. gaster's in heat. trying to help him douse the flames,” Sans called back with a grin and a wink to Gaster, who blinked back dazedly. He opened his mouth, but had no chance to say anything, as a tentacle immediately thrust inside the opening.

“...FINE, I'LL ALLOW IT! DON'T BLAME ME IF THERE'S A SECRET INGREDIENT IN THE SAUCE, THOUGH, YOU HEAR ME? AND PICK UP THE PACE! I'M HEADING OVER TO UNDYNE'S IN AN HOUR.”

“will do. you're the best, paps.” 

“MN!” Gaster hummed insistently around the tentacle in his mouth.

“gaster says thank you.”

“Mn.” Gaster's responding hum was satisfied.

“YOU'RE VERY WELCOME, GASTER. THOUGH YOUR TIMING IS VERY INCONVENIENT, YOU WERE QUITE WISE TO 'COME' TO ME, NYEH-HEH. NOW GET TO IT!”

“you heard him,” Sans said as he coaxed the tentacle Papyrus was on to move faster.

Gaster moaned.

“let's see, who's next?” Sans mused, holding up the remaining three objects.

Some tentacles thrust forward. Sans dodged backwards, but not before one of the faster tentacles slammed home in the purple object, setting a furious pace.

“oops.”

\---

Sans shoved the human he was fighting backwards as he abruptly disengaged.

The circle of humans and monsters watched him warily as he leaned on his scythe for support, head down, eyes closed, panting.

The circle flinched as he threw his head back and laughed.

“I was beginning to think he didn't have it in him, and then he goes and uses me so forcefully,” Sans said gleefully, wiping tears from his eyes. 

His eyes opened and he grinned widely, causing some of those encircling him to take a step back.

“Looks like it's you weakling's lucky day. Feel honored. You get to face the full force of my bloodlust.”

His purple eyes started to glow, blasters materializing in the air around him.

He pointed his scythe forward.

“Now...dance for me.”

\---

Sans stared for a moment before he shrugged.

“eh. he probably won't mind.”

Gaster shook his head back and forth; the tentacle slid out of his mouth with a wet pop.

“Sans, please, more,” he pleaded.

“don't worry, doc. i won't leave you hanging,” Sans soothed, reaching out to briefly cup his face before stepping back out of range of the tentacles.

Sans laughed as he noticed one tentacle furtively waving at him off to the side of the main crowd of tentacles. He reached out and stroked it; it curled lovingly around his wrist.

“you're perfect for him,” he told the tentacle, causing it to perk up as he offered the red object to it. The tentacle squeezed his wrist in an approximation of a hug before smoothly slipping deep inside.

“Yes!” Gaster hissed in pleasure.

\---

Sans twitched in his sleep, uncurling from the ball he had been in to turn onto his other side.

He sighed, arms hugging his pillow.

The pillow rubbed against his pelvis.

Moaning, he gripped it tighter as his hips moved.

\---

“one left.”

Sans stared at the remaining pale orange object in contemplation, before glancing over the remaining unoccupied tentacles. He grinned when he spotted a whole group of very thin tentacles waving in the air.

“i'm sure he'll be glad he doesn't have to pay anemone for this wonderful experience,” he said as he held the last object out to the group. The tentacles eagerly slithered inside, curling and twisting around one another.

\---

Papyrus stiffened, slowly lowering the bottle of honey.

“Something the matter, dear?” Muffet enquired, eyeing his spreading blush as he twitched.

“Yeah. Just remembered I've got-”

He jerked.

“-something to attend to.”

He dropped some gold on the counter, before abruptly standing.

With swift strides, he quickly made his way towards the exit, giving her a distracted wave of farewell as he slipped through the doorway.

Papyrus rounded the corner of Muffet's cafe and ducked into the alleyway, before teleporting to his bedroom. He leant against his closed door.

The sensations of pleasure surged, causing him to slide down to the ground as his legs turned to jelly.

“Damn,” he panted. “What kind of technique is this?”

He moaned as whatever was inside him hit the deepest part of him.

“Fuck it, I'm calling him.”

\---

When you give me k-kisses  
That's money, honey  
When I'm your lover and your mistress  
That's money, honey  
When you touch me it's so delicious  
That's money, honey  
Baby, when you tear me to pieces  
That's money, honey

Sans blinked at the music that filled the air, before he grinned, rocking back on his heels as he answered his phone.

“'sup?”

“What are you doing?” Sans was pleased to note how breathless Papyrus sounded.

“oh, not much. you?”

“Tease. Seriously, what are you doing? You've never felt like this before.”

“weeeeeell, you did say i could do whatever i wanted, whenever i wanted.”

“I did. So?”

“so gaster's magic is currently in the process of controlling him rather than the other way around--it's behaving positively cephalopodic. seeing the situation, i thought you'd enjoy helping him out.”

“Ah, so those are his moans I'm hearing in the background.”

“yep,” Sans said, glancing at the desperate expression on Gaster's face.

“hmm, still not enough, huh? papyrus, can i put you on speaker? my hands are kinda full over here. though not as full as gaster's.”

“Hah-go ahead.”

Putting his phone on Gaster's desk, Sans let his clothes fall to the floor as he stepped closer.

Sans gently moved the busy tentacles to the side, before hopping up to straddle Gaster. The chair was stopped from its backwards movement as it hit Gaster's desk.

“time for the main event.”

Sans gripped one of the thicker tentacles, guiding it to his already dripping entrance. Needing no more prompting, it plunged inside.

Sans and Gaster moaned in unison, Sans gripping Gaster's shoulders as Gaster claimed his mouth in a kiss. Finally in range, the rest of the tentacles descended upon Sans, winding through his ribs, and twining around his limbs. One tentacle slid up the side of his face, caressing just under his eye socket before pushing inside.

“oh!” Sans gasped at all the sensations rocking him this way and that.

The sound of Sans' voice caused the tentacles to react with fervor.

Sans noticed.

“that's it, just like that, so good, so deep, don't stop, keep going.”

Sans continued compliments stirred the tentacles into a frenzy.

“Yes, yes, yes,” Gaster chanted. He sloppily kissed his way along Sans' jaw, before dropping to bite Sans' neck.

“ah!”

And with that scream, everyone came undone.

\---

A torrent of nyeh-heh-hehs were released from downstairs.

\---

Sans moaned as he split his last opponent in two.

After confirming everyone who'd had the temerity to attack him was dead, he slid his hand down his pants.

Pulling his hand back out, he observed the magic that had filled him to the brim.

He smirked, amused.

“He gave me to someone else, did he? How daring~”

He licked his fingers.

“Hmm, tasty,” he purred out before he strode away, uncaring of the blood and dust that coated his boots.

\---

Sans' grunts were muffled by his grit sharp teeth as he frotted against his pillow.

Whining, he tensed, shuddering.

Slowly, his whole body relaxed, grip slackening, toes uncurling.

Sans snored on, oblivious.

\---

Listening to the sounds coming from his discarded phone, Papyrus spread his legs, panting.

Pulling up his hoodie, he threaded his fingers through his ribs, moaning as he stroked the sensitive insides in time to the writhing inside him.

Sans' scream and the resultant pulsating sensation of being stretched even further pushed him over the edge, mouth open in a silent scream as the back of his skull thunked against his door.

\---

Sans and Gaster breathed together.

Sans had been completely covered in cum. It welled from his tentacle-stuffed eye like tears, sliding down his face before dropping onto his already-drenched ribcage, which dripped intermittently onto his pelvis. He shuddered from the aftershocks as it flowed into all the holes in his sacrum, splattering off his tailbone onto Gaster's lap.

As the tentacles slowly started to dissipate, more cum gushed out of his entrance in pulses as Gaster lifted his finally-freed hands to embrace him.

“Thank you,” he rasped out, spent.

“any time, gaster.” Sans raised his voice slightly. “yo, papyrus, you still alive?”

A thud sounded from the phone.

“...Yeah, I'll live. Gonna nap.”

Sans chuckled.

“k. come over later. paps made some spaghetti.”

“'kay,” Papyrus mumbled sleepily, before ending the call as he dropped into slumber.

“...so do you think Papyrus managed to resist adding that 'secret ingredient'?” Gaster asked.

Sans laughed.

**Notes for the Chapter:**

> Putting all the different pieces of this together was a blast.
> 
> Like a puzzle. A very smut-filled puzzle. Hmm, I wonder if they make porn puzzles...
> 
> Anyways, portable pussies are the best, so I'm glad I decided to add them into this piece.
> 
> Also, shout-out to [Sugar](http://archiveofourown.org/users/BitterSweetDeath/pseuds/BitterSweetDeath) and [TCD](http://archiveofourown.org/users/trashcandisaster/pseuds/trashcandisaster) for inspiring this idea with their art and resulting conversation.
> 
> PS: UT!Sans' ringtone for US!Papyrus is Money Honey by Lady GaGa.


End file.
